The present invention relates to jigs and methods for isostatic-pressing ceramics. More particularly, this invention relates to jigs for isostatic-pressing ceramics using cavity molds for the formation of plates and methods thereof.
In manufacturing ceramics, there are a variety of shaping methods in accordance with the desired shape and the purpose of use of products. Pressing by use of metal molds is one of the shaping methods that are suitable for mass-production since it can be mechanically operated to form shaping products with excellent dimensional accuracy. In the pressing by use of metal molds, wet, semi-wet or dry raw materials for ceramics are filled into the metal mold, and pressurized to form products of a desired shape. Pressure is applied with a hand press, friction press, and hydrostatic press. When the density is low for the product obtained with pressing using metal molds, isostatic-pressing has increasingly been employed in which said product is further compacted by applying higher hydrostatic pressure after it has been sealed with air-tight rubber diaphragm.
In the conventional method for the production of plates by means of pressing, pressures of 50 to 200 kgf/cm.sup.2 are generally applied in metal molds. When higher density of products is desired, isostatic-pressing in which higher hydrostatic pressures of more than 300 kgf/cm.sup.2 are applied on the pre-pressing material in a pressure bag such as a soft, elastic rubber tube or an ice bag is followed after preliminary pressing in metal molds at pressures of 50 to 200 kgf/cm.sup.2.
When large size products such as ceramic plates are produced by the conventional pressing method, pressures of 50 to 200 kgf/cm.sup.2 obtained by a metal dye pressing are too low to give sufficient strength to the shaping green body, thus often resulting in the green body damage or wreckage during pressing operation especially when the product is removed from the mold and the shaping product not being obtainable. Namely, pressures of around 50 to 200 kgf/cm.sup.2 applied normally in the conventional metal dye pressing method are not enough to obtain large size ceramic green body because they can not give sufficient strength to the green body to avoid damages or wreckages during the removing operation and the followed handling. Therefore, it is necessary to compress even the feed powder at high pressures of more than 300 kgf/cm.sup.2 in order to provide large strength to the green body necessary for avoiding damage during pressing operation. However a large and costly system, which is industrially unpractical, is required in order to achieve the pressure higher than 300 kgf/cm.sup.2 in metal dye pressing method.